The expansion of a light gas working fluid, e.g. hydrogen or helium, at high temperature and pressure can accelerate projectiles to great velocity because of the fluid's very high speed of sound, which is proportional (in simplest form) to the square root of temperature over molecular or atomic weight. Consequently, light gas guns have a rich history dating back decades, with laboratory scale system performance matching today's best powder guns by the late 1940s, and later reaching earth escape velocity by the mid 1960s.
An older version of a missile receiving initial acceleration from a gas such as high pressure air or other gas is the subject of U.S. Pat. No. 3,583,277.
United States patent application publication 2010/0212481 discloses “[a]n improved two-stage light gas gun for launching projectiles at high speeds. The gun consists of three tubes: the expansion, pump, and launch tubes. The expansion tube contains a close-fitting expansion piston that is propelled by an explosive charge. The expansion piston in turn drives the pump piston housed within the pump tube by means of a rod connecting the two pistons. The action of the pump piston adiabatically compresses and heats a light gas of hydrogen or helium, bursting a diaphragm at a predetermined pressure and expelling the projectile from the launch tube at a very high speed.
U.S. Pat. No. 7,775,148 describes “launching payloads at high velocity uses high-pressure gas or combustion products for propulsion, with injection of high pressure gas at intervals along the path behind the payload projectile as it accelerates along the barrel of the launcher. An inner barrel has an interior diameter equal to the projectile diameter or sabot containing the projectile. An outer casing surrounds the inner barrel. Structures at intervals attach the outer casing and the inner barrel. An axial gas containment chamber (AGC) stores high pressure gas between the inner barrel wall, the outer casing wall, and enclosure bulkheads. Pressure-activated valves along the barrel sequentially release the high pressure gas contained in the AGC in to the barrel to create a [sic] continuously refreshed high energy pressure heads behind the projectile as it moves down the barrel. A frangible cover at the exit end of the barrel allows the barrel to be evacuated prior to launch. The launcher is rapidly recyclable. The valves close automatically after the projectile has exited the barrel, allowing a new projectile to be introduced into the breech and the AGC to be recharged with high-pressure gas.”
U.S. Pat. No. 7,775,148, moreover, for one embodiment states, “[t]he elongated projectile launcher barrel is supported by flotation collars near breech and muzzle ends and is erected by flooding a flotation collar near the proximal end and submerging the breech end.”
U.S. Pat. No. 6,116,136 uses recoil plates in an “actuated recoil absorbing mounting system” in order to “absorb the recoil energy from an underwater projectile launcher, such as a high discharge energy underwater gun.”
In none of the preceding patents or any other patent of which the inventors are aware are the barrels, or tubes, buoyant; is the launch tube isolated from the pump tube; or is there an automatic alignment system.
In the 1990s, Lawrence Livermore National Laboratory (LLNL) demonstrated one thousand fold scaling of this technology with a view toward its application to low cost launch of payloads to space to, for example, place satellites in orbit or stage materials for space exploration. A common feature of conventional gas guns has been the use of adiabatic compression, typically employing a piston in two (or more) stages, to produce the required high temperature, high pressure light gas. See, for example, U.S. Pat. No. 7,945,413 Koth (2011) and U.S. Pat. No. 8,201,486 Fuhrman (2012), and references cited therein. Variations on this basic approach exist as well. See, for example, U.S. Pat. No. 3,131,597 A Gram, Jr. et al. (1964) wherein a more dense fluid, in this case steam, substitutes for a solid piston. As the work at Livermore showed, managing the adiabatic compression process at large scale can be inconvenient, if not problematic, due to the large amount of energy involved, and cycling such a system to prepare for subsequent launches is time consuming.
The present inventors have previously described using hydrogen gas guns to deliver payloads to orbit in the following published articles: “Livermore Proposes Light Gas Gun For Launch of Small Payloads”, Aviation Week and Space Technology, Jul. 23, 1990, pp. 78-80; “Shooting Right For The Stars With One Gargantuan Gas Gun”, Smithsonian Magazine, January 1996, pp. 84-91; and “The Jules Verne Gun”, Popular Mechanics, December 1996, pp. 54-57. These described the construction and performance of the SHARP (Super High Altitude Research Project) launcher at LLNL as well as potentially larger follow-ons.
In addition, the present inventors in United States patent application publication 2012/0187249 A1 disclose a “pistonless” light gas launcher for placing payloads in orbit. The invention utilizes a heat exchanger for the purpose of creating in the large mass of light gas working fluid the conditions for high muzzle velocity. The current application provides additional details with respect to a heat exchanger that is well-suited to a gas gun launcher as discussed herein.
The present inventors have developed a means of launching satellites or delivering supplies to earth or lunar orbit in order to assist space exploration. The current method of delivering propellant, food and other supplies to orbit is with rocket delivery. Rocket delivery is extremely expensive with a typical cost of about $5,000-$10,000 per lb of payload delivered. The requirement for approximately 9 km s−1 ΔV to attain earth orbit when coupled with the rocket equation yields only a few percent payload fraction for rocket delivery. The inventors' method uses a hydrogen gas gun to first boost a rocket to high speed. This allows a smaller more efficient rocket to deliver the payload to orbit. The payload fractions obtained are thereby much higher than obtained by a rocket alone. The higher payload fractions plus the re-usable hydrogen gas gun, whose cost is amortized over many launches, reduce the payload delivery cost by more than a factor of 10.